Bobb-Semple Dara, Zeng Li, Cordova Isvar, Bergsman David S, Nordlund Dennis, Bent Stacey F
Department of Chemical Engineering, Stanford University, Stanford, California 94305-5025, United States.
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
Langmuir. 2020 Nov 3;36(43):12849-12857. doi: 10.1021/acs.langmuir.0c01974. Epub 2020 Oct 20.
For years, many efforts in area selective atomic layer deposition (AS-ALD) have focused on trying to achieve high-quality self-assembled monolayers (SAMs), which have been shown by a number of studies to be effective for blocking deposition. Herein, we show that in some cases where a densely packed SAM is not formed, significant ALD inhibition may still be realized. The formation of octadecylphosphonic acid (ODPA) SAMs was evaluated on four metal substrates: Cu, Co, W, and Ru. The molecular orientation, chain packing, and relative surface coverage were evaluated using near-edge X-ray absorption fine structure (NEXAFS), Fourier transform infrared (FTIR) spectroscopy, and electrochemical impedance spectroscopy (EIS). ODPA SAMs formed on Co, Cu, and W showed strong angular dependence of the NEXAFS signal whereas ODPA on Ru did not, suggesting a disordered layer was formed on Ru. Additionally, EIS and FTIR spectroscopy confirmed that Co and Cu form densely packed, "crystal-like" SAMs whereas Ru and W form less dense monolayers, a surprising result since W-ODPA was previously shown to inhibit the ALD of ZnO and AlO best among all the substrates. This work suggests that multiple factors play a role in SAM-based AS-ALD, not just the SAM quality. Therefore, metrological averaging techniques (e.g., WCA and FTIR spectroscopy) commonly used for evaluating SAMs to predict their suitability for ALD inhibition should be supplemented by more atomically sensitive methods. Finally, it highlights important considerations for describing the mechanism of SAM-based selective ALD.
多年来，区域选择性原子层沉积（AS-ALD）领域的许多努力都集中在试图获得高质量的自组装单分子层（SAMs）上，多项研究表明这些单分子层对阻止沉积是有效的。在此，我们表明，在某些未形成密集堆积的SAMs的情况下，仍然可以实现显著的ALD抑制。在四种金属衬底（铜、钴、钨和钌）上评估了十八烷基膦酸（ODPA）SAMs的形成情况。使用近边X射线吸收精细结构（NEXAFS）、傅里叶变换红外（FTIR）光谱和电化学阻抗谱（EIS）对分子取向、链堆积和相对表面覆盖率进行了评估。在钴、铜和钨上形成的ODPA SAMs显示出NEXAFS信号的强烈角度依赖性，而在钌上的ODPA则没有，这表明在钌上形成了无序层。此外，EIS和FTIR光谱证实，钴和铜形成了密集堆积的“晶体状”SAMs，而钌和钨形成的单分子层密度较小，这是一个令人惊讶的结果，因为之前在所有衬底中，W-ODPA对ZnO和AlO的ALD抑制效果最佳。这项工作表明，在基于SAM的AS-ALD中，多种因素都起作用，而不仅仅是SAM的质量。因此，通常用于评估SAMs以预测其对ALD抑制适用性的计量平均技术（如WCA和FTIR光谱）应辅以更具原子敏感性的方法。最后，它突出了描述基于SAM的选择性ALD机制的重要考虑因素。
